Use of "their" referencing a singular noun -- e.g. "A teacher should put their stuff away here" rather than "A teacher should put his/her stuff here" (ironically, I just saw that on this thread).

There's nothing grammatically wrong with using the singular 'they', particularly when it's about a generic not a specific teacher (to take your example), and there's an indeterminate number of them. Preferring 'his/her' or 'his or her' is a matter of style, rather than grammar.

The word "paid" seems to have disappeared, to be replaced with "payed". I'm not sure if this is something I'd really object to, it just jars me each time I see it. I suppose it's my brain fighting itself whether it's right or not - "They put "ed" after the verb! That's right - NOOOO! It's an irregular standard spelling! That's wrong!"

"I feel sarcasm is the lowest form of wit." "It is so low, in fact, that Miss Manners feels sure you would not want to resort to it yourself, even in your own defense. We do not believe in retaliatory rudeness." Judith Martin

Perhaps not pure grammar and straying more into the realm of "wrond word, cuss it all to tarnation!", but certainly a problem with near homophones:

'Making due' for 'making do' which used to flummox me a bit until I realised that in US pronunciation 'due' and 'do' sound very alike. In British English, 'due' is pronounced somewhere closer to 'jew', so the two words are never mixed up.

"Changing tact" for "changing tack". It's a nautical term for changing direction by putting the bow into the wind. Changing 'tact' doesn't make any sense.

"Cue" instead of "queue" . Occasionally I've seen "que" used as, perhaps, a gesture in the right direction!

And a final confusion : there are a large number of people who can't differentiate between 'imply' and 'infer'. That's an annoying one.

Use of "their" referencing a singular noun -- e.g. "A teacher should put their stuff away here" rather than "A teacher should put his/her stuff here" (ironically, I just saw that on this thread).

There's nothing grammatically wrong with using the singular 'they', particularly when it's about a generic not a specific teacher (to take your example), and there's an indeterminate number of them. Preferring 'his/her' or 'his or her' is a matter of style, rather than grammar.

Shakespeare used it. That's good enough for me.

Wow, learn something new every day! I just googled it, and apparently there's also an origin of this attached to the feminist movement, because "he" was the commonly accepted singular form of this.

Anyway, my vote for #1 annoyance is apostrophe abuse, mainly because it seems to be growing at an epic rate.

Using 'them' instead of 'those' may be intended to be humorous. We all know the phrase, 'How do you like them apples?' as a jocular put-down. It can also be used as an intensive as, 'I sure would like to get me some of them there apples!'. Everyone knows it's not correct but will use it from time to time.

It's not used that way in the UK, or at least not commonly. Unfortunately the incorrect - and obviously incorrect, not jocular but just in the normal flow of conversation - use is spreading.

For all that I try my best to spell check, for all that I try my best to remember basic grammar rules, I probably still, and will always look like a caveman bashing at a keyboard to someone somewhere. So, when I make mention here of some of the things that make my eye twitch, I'm fully aware that I'm guilty of some of the egregious sins that cause others to wince.

My biggest (minor) annoyances are when people use words that either don't exist or they use a word that to them maybe sounds similar to the word they're actually meaning to use, but it's the wrong word. I came to find out that the latter actually has a word! It's called catachresis or malapropism. And it drives me nuts. (Hey, I've started a sentence with "and." I knew I'd catch a sin here or there.) An example would be someone saying, "This is such flagrant food." I'd have to assume they meant flavorful, or even fragrant, but flagrant food? You've got me there, buddy, perhaps the food is shockingly noticeable.

Lastly, I think that some people might find this David Mitchell Soapbox amusing, and appropriate!: http://www.youtube.com/watch?v=kge9ZzjsfW8&feature=plcp *The usual warnings apply. It's a YouTube page, so there may be swearing or inappropriate items on the page. The rant, however, is remarkably free from such things.*

Perhaps not pure grammar and straying more into the realm of "wrond word, cuss it all to tarnation!", but certainly a problem with near homophones:

'Making due' for 'making do' which used to flummox me a bit until I realised that in US pronunciation 'due' and 'do' sound very alike. In British English, 'due' is pronounced somewhere closer to 'jew', so the two words are never mixed up.

"Changing tact" for "changing tack". It's a nautical term for changing direction by putting the bow into the wind. Changing 'tact' doesn't make any sense.

"Cue" instead of "queue" . Occasionally I've seen "que" used as, perhaps, a gesture in the right direction!

And a final confusion : there are a large number of people who can't differentiate between 'imply' and 'infer'. That's an annoying one.

Changing tact makes perfect sense to me. I am changing the tact I used to approach something. For example, being sensitive to one aspect may have not worked, so I become sensitive to something else and have thus changed my tact.

The one that absolutely blows my mind is the possessive of "I". College educated people saying, "John and I's paper," makes me stabby! When was anyone anywhere ever taught that?

I spend a lot of time around writers, so I don't see as many of the "alot" or "there/their" type of issues, but I do get frustrated when people don't understand there are different types of writing. It's like they internalize every writing rule they've ever heard and then insist on never breaking them ever. I feel that there's a lot of leeway in most types of writing - some rules are followed for academic writing but not for fiction, others are for narrative but not dialogue, others are for one mood but not another.

The biggest of these issues seem to be sentence fragments and passive voice. Neither are wrong! Academic writing is full of passive voice - that's how you're supposed to do it! Yes, it slows down your writing - but sometimes that's the effect you want. "The diamonds were in the safe" focuses on the diamonds; "the safe held the diamonds" focuses on the safe. Two different meanings. Sentence fragments are important, too, if you want a punchier feel.

After seeing a fair sampling of the types of manuscripts actual editors see every day, though, I get the feeling most editors would settle for just having writers know its/it's and how to make new paragraphs properly

Changing tact makes perfect sense to me. I am changing the tact I used to approach something. For example, being sensitive to one aspect may have not worked, so I become sensitive to something else and have thus changed my tact.

But 'tact' isn't defined as having different kinds or qualities. I've never seen it as having any sort of qualifier or adjective that would suggest you get different kinds. It is, simply, being sensitive to what's appropriate in dealing with other people or situations. So if your approach, being sensitive to one aspect, hasn't worked and you change the way you deal with the situation, you aren't changing by being sensitive to something else or changing tact, you are just **changing your approach** to how you deal with the person or the situation by using the same sensitivity, the same tact. You're just trying a new way of doing it.